A, longitudinal section of bone, by which the Haversian canals are seen
     branching and communicating with one another;
  B, cross section of a very thin slice of bone, magnified about 300
     diameters—­little openings (Haversian canals) are seen, and around
     them are ranged rings of bones with little black bodies (lacunae), from
     which branch out fine dark lines (canaliculi);
  C, a bone cell, highly magnified, lying in lacuna.
]

The Bones of the Head.

31.  The Head, or Skull.  The bones of the skeleton, the bony framework of our bodies, may be divided into those of the head, the trunk, and the limbs.

The bones of the head are described in two parts,—­those of the cranium, or brain-case, and those of the face.  Taken together, they form the skull.  The head is usually said to contain 22 bones, of which 8 belong to the cranium and 14 to the face.  In early childhood, the bones of the head are separate to allow the brain to expand; but as we grow older they gradually unite, the better to protect the delicate brain tissue.

32.  The Cranium.  The cranium is a dome-like structure, made up in the adult of 8 distinct bones firmly locked together.  These bones are: 

  One Frontal,
  Two Parietal,
  Two Temporal
  One Occipital,
  One Sphenoid,
  One Ethmoid.

The frontal bone forms the forehead and front of the head.  It is united with the two parietal bones behind, and extends over the forehead to make the roofs of the sockets of the eyes.  It is this bone which, in many races of man, gives a dignity of person and a beauty of form seen in no other animal.

The parietal bones form the sides and roof of the skull.  They are bounded anteriorly by the frontal bone, posteriorly by the occipital, and laterally by the temporal and sphenoid bones.  The two bones make a beautiful arch to aid in the protection of the brain.

The temporal bones, forming the temples on either side, are attached to the sphenoid bone in front, the parietals above, and the occipital behind.  In each temporal bone is the cavity containing the organs of hearing.  These bones are so called because the hair usually first turns gray over them.

The occipital bone forms the lower part of the base of the skull, as well as the back of the head.  It is a broad, curved bone, and rests on the topmost vertebra (atlas) of the backbone; its lower part is pierced by a large oval opening called the foramen magnum, through which the spinal cord passes from the brain (Fig. 15).

The sphenoid bone is in front of the occipital, forming a part of the base of the skull.  It is wedged between the bones of the face and those of the cranium, and locks together fourteen different bones.  It bears a remarkable resemblance to a bat with extended wings, and forms a series of girders to the arches of the cranium.

The ethmoid bone is situated between the bones of the cranium and those of the face, just at the root of the nose.  It forms a part of the floor of the cranium.  It is a delicate, spongy bone, and is so called because it is perforated with numerous holes like a sieve, through which the nerves of smell pass from the brain to the nose.